Rechargeable batteries are typically charged by a source of constant voltage/constant current CV/CC) with crossover voltage, e.g., 3.7 V. Initially the battery is charged using a constant current (i.e., in CC mode) until the crossover point is reached (e.g., 3.7V), at which point the charger switches to constant voltage mode to maintain the voltage at the terminal of the rechargeable battery at substantially about the crossover voltage. The charging period required to achieve 90-100% capacity is typically 2-4 h, with the CC stage being around 40 minutes at 1 C charging rate (i.e., a charging rate corresponding to a charging current level that would charge a battery in one hour). Generally, at the conclusion of the CC stage the rechargeable battery achieves a charge level of 60-70% of the charge capacity of the battery. The CV stage of the charging process generally take 1-3 hours to complete. During that time the charging current level decreases and typically reaches a level corresponding to a charge rate of 0.1 C by the time the charging process is concluded.
One factor limiting the expediency of the charging rechargeable batteries is the danger of causing the charger and/or battery to overheat. Such overheating may damage the charger and/or battery, and further pose a safety risk. Consequently, conventional chargers are configured to apply charging current corresponding to charge rates of about 1 C. To protect against overheating conditions, temperature sensors are sometimes used to monitor the temperature of the charger and/or the battery, thus enabling the charger to undertake remedial or preemptive actions in the event of the detection of overheating conditions (e.g., terminating the charging current if the battery's temperature exceeds a safety limit of, for example, 45° C.)